Moments, cross-products and summing moments

2.Cross product of two vectors or finding y and x components and multiplying each by appropriate distance (then adding them up to find moment)

3. Ok im confused about how to even approach the problem. If someone tells me where the axis are and how i have to look at teh problem im sure I can do it. But i have no clue where and how to look at the problem

for the first one (a) I made this diagram

so according to taht the x component of that A weight will be not effecting anything since distance will be 0 but y component which is